The service life of dental composite restorations averages 7 years. The main causes for replacement are secondary caries and fracture. Some controlled clinical studies, for mostly conservative composite restorations, show survivals of 10-20 years. But data from cross-sectional and other controlled studies prove that current formulations are not adequately stable. Material degradation over time in the mouth, coupled with variations in microflora and caries risk in certain patients, greatly contributes to reduced service life.
While most of the improvements in composites have come from altering the filler technology, recently new monomers have been developed to decrease polymerization shrinkage and its associated stress. However, most still rely on resin matrices with methacrylate chemistry. The main disadvantage of methacrylates is the relatively low resistance to degradation by hydrolysis and enzymatic attack by esterases, leading to breakdown of the restorative material and the composite/tooth interface. Therefore, there is an urgent need to develop new composites based on more stable compounds, while at the same time maintaining or exceeding the mechanical properties and shrinkage/stress behavior of current commercial materials.
Methacrylate monomers have been used as the main constituents in the resin matrix in composite materials for over 50 years. Their relative success derives from excellent aesthetic properties, convenient and fast cure on command, rigidity similar to dentin, and mechanical stability. Despite these aspects, there are significant negative attributes that limit their longevity in the oral cavity, such as high shrinkage and accompanying stress, lower than desirable fracture toughness, relatively low degree of conversion (DC), and high rate of degradation by hydrolysis and enzymatic attack of the resin matrix and the composite/tooth interfacial bond. The goal of this proposal is to develop novel resin systems that will maintain or improve upon the beneficial assets while addressing the shortcomings of methacrylates.
Many available monomers, such as epoxies, vinyl ethers, allyl ethers, maleimides or (meth)acrylamides, may offer greater resistance to hydrolytic/enzymatic attack than methacrylates.